This invention relates in general to apparatus for chemically cutting objects within a well bore and in particular to apparatus for chemically cutting objects within a well bore which include means for selectively venting the pressure within the tool while the tool is still within the well bore.
Chemical cutting devices or tools are well known within the prior art and are frequently utilized to cut, sever, perforate or slot an object within a well bore. The objects referred to above may include metal pipe, well bore casing, earth formations or foreign objects such as lost tools which may be found within the well bore.
Such known devices are typically tubular casings which enclose a chamber of a chemical cutting fluid which is extremely active chemically and which reacts violently when brought into contact with most oxidizable substances. Examples of such cutting fluids include fluorine and the halogen fluorides including such compounds as chlorine trifluoride, chlorine monofluoride, bromine trifluoride, bromine pentafluoride, iodine pentafluoride and iodine hextafluoride in mixtures thereof.
Generally stated, chemical cutting fluids of a character such as are described above are introduced into a well bore in a confined chamber within a tubular casing and the fluid is caused to discharge from the tubular casing in one or more high velocity streams or jets by applying to the chamber a suitable pressurizing agent. Pressurizing agents known in the prior art include hydraulic or pneumatic fluids. Pneumatic fluids may be gases generated by ignition of one of the various types of relatively slow burning gunpowders or other deflagrating types of explosives including black powder, rocket propellant powders or the like. By appropriate selection of an explosive and by means of preparation procedures well known to those skilled in the art of such explosives, the ignition and burning rates of such explosives may be effectively controlled to generate gases at any desired rate and volume suitable for applying the desired pressurizing forces to the confined chamber of cutting fluid.
Another well known feature of these chemical cutting tools includes the utilization of pressure operated slips or anchors which are utilized to retain the tool in a selected position during operation of the chemical cutting fluid. These devices typically operate in reponse to pressure within the tubular casing caused by actuation of an explosive charge or other pressurizing medium and erect outward from the periphery of the tubular casing to lock the tool in position during operation. A problem which has been noted in known chemical tools involves the frequent occurrence wherein the discharge passage becomes clogged after a cutting operation has occurred. When the tool is withdrawn, the pressure within the tool cannot discharge and the hydrostatic pressure in the well bore becomes substantially lower than the internal pressure of the tool. The slips or anchors which are utilized to maintain the tool in position respond to this pressure by erecting and anchoring the tool in place, rendering the tool difficult if not impossible to remove without damage to the tool or the casing. Thus, it should be apparent to those ordinarily skilled in the art that a need has existed for a chemical cutting tool which includes a means for selectively venting or bleeding off built up pressure within a tool which occurs as a result of a clogged discharge passage.